Split schema.graphql and schema.resolvers.go into per-domain files

Move Query/Mutation field declarations from the monolithic schema.graphql
into each domain's .graphql file using extend type, so gqlgen places
resolvers in the matching *.resolvers.go files. Extract helper functions
into *_helpers.go files to prevent gqlgen from commenting them out.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/graph/gitea.resolvers.go

@@ -1,5 +1,10 @@
 package graph
 
+// This file will be automatically regenerated based on the schema, any resolver
+// implementations
+// will be copied through when generating and any unknown code will be moved to the end.
+// Code generated by github.com/99designs/gqlgen version v0.17.88
+
 import (
 	"context"
 	"time"
@@ -8,17 +13,6 @@ import (
 	"adam-french.co.uk/backend/services"
 )
 
-func mapGiteaFeed(feed *services.GiteaFeedResponse) *model.GiteaFeedItem {
-	return &model.GiteaFeedItem{
-		AvatarURL:     feed.ActUser.AvatarURL,
-		RepoURL:       feed.Repo.HTMLURL,
-		RepoName:      feed.Repo.FullName,
-		OpType:        feed.OpType,
-		CommitMessage: services.ParseCommitMessage(feed.Content),
-		CreatedAt:     feed.Created,
-	}
-}
-
 // GiteaFeed is the resolver for the giteaFeed field.
 func (r *queryResolver) GiteaFeed(ctx context.Context) (*model.GiteaFeedItem, error) {
 	if r.Store.GiteaFeedFresh() {